Ultrasonic probe

Abstract

The present invention provides an ultrasonic probe with a novel configuration, comprising an acoustic lens made of polymethylpentene with one concave surface, and an acoustic propagation medium in the concave space resulting from the concave surface. [Solution] The ultrasonic probe 10 includes an ultrasonic propagation medium 11e which is made of a gel-like urethane having an attenuation rate of 0.5 to 4 dB / mm, an acoustic impedance of 1.45 to 1.65 MRayl, and a sound velocity slower than the sound velocity of polymerylpentene. However, the attenuation rate is measured at an ultrasonic frequency of 10 MHz. The gel-like urethane is made of a mixture of soft urethane and a plasticizer with a specific gravity of 0.9 to 1.4 g / cc.

Description

Technical Field

[0004]

[0001] The present invention relates to an ultrasonic probe particularly suitable for use in ultrasonic examinations of the human body.

Background Art

[0002] A typical ultrasonic probe includes members such as an acoustic lens, an acoustic matching layer, and a transducer array in this order when viewed from the human body side. In order to improve the characteristics of the ultrasonic probe, it is necessary to consider the acoustic impedance matching between the human body and the respective members of the ultrasonic probe, the magnitude relationship of the sound velocities of the human body and the respective members of the ultrasonic probe, the attenuation rate of the respective members, and the like. The acoustic impedance of the human body is about 1.6 MRay. Since polymethylpentene has an acoustic impedance of 1.65 to 1.75 MRay, which is close to that of the human body, and its safety for the human body is also recognized, it is preferable as a constituent material of the acoustic lens.

[0003] On the other hand, in order to improve the contact property of the ultrasonic probe with the human body, the surface of the acoustic lens on the human body side may be a flat surface or a convex surface. In that case, considering ensuring the convergence of ultrasonic waves due to the sound velocity in the human body being about 1500 m / sec and the sound velocity in polymethylpentene being about 2000 m / sec, and simplifying the structure of the probe, the surface of the acoustic lens on the acoustic matching layer side is made concave. An example thereof is described in, for example, the third embodiment and FIG. 4 of Patent Document 1. And in the case of the third embodiment of Patent Document 1, an ultrasonic propagation medium made of synthetic rubber such as butadiene rubber is provided in the concave space generated between the acoustic matching layer and the acoustic lens due to the concave surface. As the ultrasonic flaw detector becomes for high frequencies, and the acoustic lens is increasingly made of a plastic material such as polymethylpentene, the above ultrasonic propagation medium is useful for reducing the attenuation rate of the ultrasonic probe and the like (lines 10 to 17 in the upper right column on page 4 of Patent Document 1).

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 62-233149 [Overview of the project] [Problems that the invention aims to solve]

[0005] It is considered useful to provide an ultrasonic propagation medium in the concave space created between the acoustic matching layer and the acoustic lens. Furthermore, if the above-mentioned ultrasonic propagation medium can be constructed from a material other than synthetic rubber, it would be preferable as it would increase the design flexibility of the ultrasonic probe. The inventor of this application has conducted research from this perspective and has completed the present invention. This application has been made in view of the above points, and therefore the object of this application is to provide an ultrasonic probe with a novel configuration comprising an acoustic lens made of polymethylpentene with one surface being concave, and an acoustic propagation medium in a concave space resulting from the concave surface. [Means for solving the problem]

[0006] To achieve this objective, the present invention is characterized by comprising: an acoustic lens made of polymethylpentene with one surface being concave; an acoustic matching layer bonded to the acoustic lens on the concave side; and an ultrasonic propagation medium provided in a recessed space between the acoustic lens and the acoustic matching layer caused by the concave surface, the ultrasonic propagation medium being made of a gel-like urethane with an attenuation rate of 0.5 to 4 dB / mm, an acoustic impedance of 1.45 to 1.65 MRayl, and a sound velocity slower than the sound velocity of polymethylpentene (provided that the attenuation rate is measured at an ultrasonic frequency of 10 MHz). [Effects of the Invention]

[0007] The ultrasonic probe of this invention uses a predetermined gel-like urethane as the ultrasonic propagation medium provided in the concave space between the acoustic lens and the acoustic matching layer. As a result, as can be seen from the experimental results described later, an ultrasonic probe with improved ultrasonic attenuation is obtained compared to a general ultrasonic probe in which the acoustic lens is made of silicone rubber. Moreover, because it is gel-like, it has better filling properties into the concave space compared to when the ultrasonic propagation medium is made of rigid rubber or other hard materials, and therefore the adhesion with the acoustic lens and acoustic matching layer surrounding the concave space is also improved. Furthermore, by, for example, incorporating a plasticizer into soft urethane and adjusting the composition (specific gravity, sound velocity) and content of the plasticizer, an ultrasonic propagation medium with the attenuation rate, acoustic impedance, and sound velocity required in this invention can be realized, thus enabling the creation of an ultrasonic flaw detector that meets the desired specifications. Therefore, it is possible to provide an ultrasonic probe with a novel configuration that includes an acoustic lens made of polymethylpentene with one surface being concave, and an ultrasonic wave propagation medium in the concave space resulting from the concave surface. [Brief explanation of the drawing]

[0008] [Figure 1] (A) is a diagram illustrating an ultrasonic probe 10 of an embodiment, (B) is a diagram illustrating a key part 11 of the present invention provided inside the ultrasonic probe 10, and (C) is a diagram illustrating a modified example of the barrier layer. [Figure 2] (A) is a diagram illustrating the difference in sensitivity between the ultrasonic probe 10 of the embodiment and a conventional ultrasonic probe in which the acoustic lens is made of silicone rubber, and (B) is a diagram illustrating the frequency characteristics of the sensitivity of both. [Modes for carrying out the invention]

[0009] Embodiments of this invention will be described below with reference to the drawings. Note that the figures used in this description are only schematic representations to the extent necessary to understand the invention. Furthermore, in the figures used in this description, similar components are indicated with the same number, and their descriptions may be omitted. Also, the shapes, materials, etc., described in the following embodiments are merely preferred examples within the scope of this invention. Therefore, the present invention is not limited to the following embodiments.

[0010] First, the configuration of the ultrasonic probe 10 of the embodiment will be described with reference to Figure 1. Figure 1(A) is a diagram showing an example of the external shape of the ultrasonic probe 10 of the embodiment, and Figures 1(B) and (C) are cross-sectional views illustrating the main parts 11 of the present invention provided inside the ultrasonic probe 10 of the embodiment. However, in Figures 1(B) and (C), some of the hatching indicating the cross-section has been omitted. Also, in Figure 1(A), an ultrasonic diagnostic device 7 connected to the ultrasonic probe is also shown. Furthermore, Figures 1(B) and (C) are diagrams corresponding to cross-sections of Figure 1(A) cut in a direction parallel to the plane of the paper. As shown in Figure 1(B), the ultrasonic probe 10 of this embodiment comprises, in order from the subject (human body) 20 side, an acoustic lens 11a, an acoustic matching layer 11b, a transducer array 11c, and a backing layer 11d. Each of the acoustic matching layer 11b, transducer array 11c, and backing layer 11d can be made of conventionally known materials according to the specifications required for the ultrasonic probe 10. The acoustic matching layer 11b may be a single layer or multiple layers. This ultrasonic probe 10 further includes the following features as a characteristic of the present invention. Specifically, the acoustic lens 11a is made of polymethylpentene, and the surface of the acoustic lens 11a facing the acoustic matching layer 11b is a concave surface 11aa, which is concave toward the center in the thickness direction of the acoustic lens. A predetermined ultrasonic propagation medium 11e, described later, is provided in the recessed space between the acoustic lens 11a and the acoustic matching layer 11b, which is caused by this concave surface 11aa.

[0011] The specified ultrasonic propagation medium 11e is made of a gel-like urethane with an attenuation rate of 0.5 to 4 dB / mm, an acoustic impedance of 1.45 to 1.65 MRayl, and a sound velocity slower than the sound velocity of polymerylpentene. However, the attenuation rate is measured at an ultrasonic frequency of 10 MHz. The reasons for requiring the attenuation rate, acoustic impedance, and sound velocity of the ultrasonic propagation medium 11e as described above are as follows. The reasons for requiring an attenuation rate of 0.5 to 4 dB / mm for the ultrasonic propagation medium 11e are: a. a smaller attenuation rate is better; b. the attenuation rate of silicone rubber, which is widely used in the manufacture of ultrasonic probes, is about 4 dB / mm; c. as will be described later, the gel-like urethane used in the present invention can be realized by a mixture of soft urethane and a predetermined plasticizer, but the attenuation rate of soft urethane alone is about 3.7 dB / mm, and by increasing the plasticizer content, the attenuation rate can be reduced to about 0.5 dB / mm. Taking all of these into consideration, an attenuation rate of 0.5 to 4 dB / mm is considered good.

[0012] Furthermore, the reason for requiring an acoustic impedance of 1.45 to 1.65 MRay for the ultrasonic propagation medium 11e is that the acoustic impedance of polymethylpentene is approximately 1.66 to 1.8, and it is desirable to match this as closely as possible. Additionally, this range is considered appropriate when considering the achievable acoustic impedance when obtaining the ultrasonic propagation medium 11e using a mixture of soft urethane and a plasticizer. Furthermore, the sound velocity of the ultrasonic propagation medium 11e is set to a sound velocity slower than the sound velocity of polymerylpentene. The reason for this requirement is to focus the ultrasound as desired.

[0013] Such an ultrasonic propagation medium 11e can be composed of, for example, a mixture of soft urethane and a plasticizer with a specific gravity of 0.9 to 1.4 g / cc. As the plasticizer, for example, an organic gel expander can be used. The organic gel expander is not limited to this, but for example, propylene carbonate can be used. The soft urethane is preferably a soft urethane with a Shore E hardness in the range of 30 to a consistency of 300. Using a soft urethane in this range makes it easier to realize an ultrasonic propagation medium with an attenuation rate within the desired range as defined in this invention. Furthermore, the amount of plasticizer mixed into the soft urethane should be selected within the range of 10 to 50 parts by weight. If the plasticizer content is too high, plasticizer bleed-out is more likely to occur, and if it is too low, the effect of reducing the ultrasonic attenuation rate of the ultrasonic propagation medium will be reduced. Considering these factors, the above range is preferable.

[0014] Furthermore, the ultrasonic probe 10 of this embodiment is equipped with a barrier layer 11f between the ultrasonic propagation medium 11e and the acoustic lens 11a to prevent the plasticizer in the ultrasonic propagation medium 11e from bleeding out. Specifically, in the example shown in Figure 1(B), a barrier layer 11f is provided between the ultrasonic propagation medium 11e and the acoustic lens 11a. In the example shown in Figure 1(C), in addition to the structure of Figure 1(B), a barrier layer 11f is also provided between the ultrasonic propagation medium 11e and the acoustic matching layer 11b. The barrier layer 11f can be made of any suitable material, as long as it can suppress plasticizer bleed-out and does not impair the characteristics of the ultrasonic probe 10. For example, it can be made of a metal film such as a gold film or a silver film, or an inorganic material such as a film with silica deposited on it. If plasticizer bleed-out occurs, the composition of the ultrasonic propagation medium 11e may change, altering the propagation of ultrasound and potentially degrading the characteristics of the ultrasonic transducer. Therefore, it is preferable to provide a barrier layer 11f.

[0015] The main component 11, comprising the acoustic lens 11a, acoustic matching layer 11b, transducer array 11c, backing layer 11d, ultrasonic propagation medium 11e, and barrier layer 11f, is housed in a case 13, as shown in Figure 1(A). A cable 15 is routed from the main component 11 to the outside of the case 13, and the other end of the cable 15 is connected to the diagnostic imaging device 17 via a predetermined connector (not shown). Note that the shape of the case 13 and the cable 15 are examples and can be made as desired depending on the specifications of the ultrasonic probe and the diagnostic imaging device.

[0016] (Example) As the acoustic lens 11a, an acoustic lens made of polymethylpentene and having a concave surface 11aa on one surface was prepared. The polymethylpentene used had an attenuation rate of 1.8 dB / mm at 10 MHz, a sound velocity of 2100 m / sec, and an acoustic impedance of 1.75 MRay. Also, the curvature of the concave surface 11aa was set such that the focal length of the acoustic lens 11a was 15 mm. Predetermined ones were prepared as the acoustic matching layer 11b, the transducer array 11c, and the backing layer 11d. As the ultrasonic propagation medium 11e, the following was prepared. That is, a soft urethane having a Shore E hardness of 30 to 350 and a hardness of 37, an attenuation rate of 3.7 dB / mm at 10 MHz, and an acoustic impedance of 1.5 MRay was prepared. Also, propylene carbonate (having a specific gravity of 1.2 g) was prepared as a plasticizer. Then, a mixture obtained by mixing propylene carbonate with this soft urethane at a ratio of 25 parts by weight was prepared, and the ultrasonic propagation medium 11e was formed using this. The thus prototyped ultrasonic propagation medium had an attenuation rate of 1.7 dB / mm at 10 MHz and an acoustic impedance of 1.6 MRay. Then, these acoustic lens 11a, ultrasonic propagation medium 11e, predetermined acoustic matching layer 11b, transducer array 11c, backing layer 11d, electrodes, etc. were arranged and formed so as to be the main part 11 of the ultrasonic probe shown in Fig. 1(B). In this example, the barrier layer 11f was not provided.

[0017] The evaluation of the ultrasonic probe of the embodiment formed as described above was conducted as follows. That is, in an aqueous medium, an aluminum object installed at a distance of 15 mm from the prototype ultrasonic probe was irradiated with ultrasonic waves to cause reflection, and the received voltage sensitivity of the ultrasonic waves was measured. The measurement results are shown in Fig. 2. Fig. 2(A) shows the received voltage characteristics, and Fig. 2(B) shows the frequency characteristics of the received voltage. In addition, in each characteristic diagram of Fig. 2(A) and (B), as a comparative example, the characteristics of an ultrasonic probe having an acoustic lens formed of silicone rubber that has been generally used are also shown. In each figure, the solid line represents the characteristics of the embodiment, and the dashed line represents the characteristics of the comparative example. Since the prototype ultrasonic probe is assumed to emit ultrasonic waves of 10 MHz, the vicinity of 10 MHz in the spectrum is particularly important for evaluation.

[0018] From the characteristic diagram of Fig. 2(A), it can be seen that in the case of the ultrasonic probe of the embodiment, the received voltage sensitivity is equal to or higher than that of the comparative example. Specifically, in terms of the actually measured value, it can be seen that S1 - S2 = 5.4 dB has been improved. Also, from the characteristic diagram of Fig. 2(B), it can be seen that in the desired frequency band, here the band around 10 MHz, the received voltage sensitivity is equal to or higher than that of the comparative example, and furthermore, it can be seen that it has been improved. Therefore, according to the present invention, it can be seen that an ultrasonic probe with a novel configuration that includes an acoustic lens made of polymethylpentene and having one concave surface, and an acoustic propagation medium in the concave space caused by the concave surface can provide a practical ultrasonic probe.

Explanation of Reference Signs

[0019] 10: Ultrasonic probe of the embodiment 11a: Acoustic lens 11aa: Concave surface 11b: Acoustic matching 11c: Transducer array 11d: Backing layer 11f: Barrier layer 20: Specimen

Claims

1. An ultrasonic probe characterized by comprising: an acoustic lens made of polymethylpentene with one surface being concave; an acoustic matching layer bonded to the acoustic lens on the concave side; and an ultrasonic propagation medium provided in a recessed space between the acoustic lens and the acoustic matching layer caused by the concave surface, the ultrasonic propagation medium being made of a gel-like urethane having an attenuation rate of 0.5 to 4 dB / mm, an acoustic impedance of 1.45 to 1.65 MRayl, and a sound velocity slower than the sound velocity of polymethylpentene (provided that the attenuation rate is measured at an ultrasonic frequency of 10 MHz).

2. The ultrasonic probe according to claim 1, characterized in that the gel-like urethane is composed of a mixture of soft urethane and a plasticizer with a specific gravity of 0.9 to 1.4 g / cc.

3. The ultrasonic probe according to claim 2, characterized in that at least the ultrasonic transmission medium and the acoustic lens are provided with a barrier layer to prevent the plasticizer from bleeding out.

4. The ultrasonic probe according to claim 2 or 3, characterized in that the soft urethane is a soft urethane with a Shore E hardness of 30 to 350.

5. The ultrasonic probe according to claim 2, characterized in that the plasticizer is propylene carbonate.

6. The ultrasonic probe according to claim 2, 3, or 5, characterized in that the plasticizer content is 10 to 50 parts by weight.

7. An acoustic lens made of polymethylpentene with one surface being concave, The acoustic matching layer bonded to the acoustic lens on the concave side, An ultrasonic propagation medium provided in a recessed space between the acoustic lens and the acoustic matching layer caused by the concave surface, comprising a gel-like urethane having an attenuation rate of 0.5 to 4 dB / mm, an acoustic impedance of 1.45 to 1.65 MRayl, and a sound velocity slower than the sound velocity of polymerylpentene, The ultrasonic propagation medium is composed of a mixture of soft urethane and a plasticizer with a specific gravity of 0.9 to 1.4 g / cc contained in the soft urethane. The ultrasonic probe is characterized in that the soft urethane is a soft urethane with a Shore E hardness of 30 to 350.

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